[PATCH] SVM: reliably detect if SVM was disabled by BIOS

[PATCH] SVM: reliably detect if SVM was disabled by BIOS

[Joerg Roedel]

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From: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>

This patch adds an implementation to the svm is_disabled function to
detect reliably if the BIOS disabled the SVM feature in the CPU. This
fixes the issues with kernel panics when loading the kvm-amd module on
machines where SVM is available but disabled.

Signed-off-by: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>

-- 
           |           AMD Saxony Limited Liability Company & Co. KG
 Operating |         Wilschdorfer Landstr. 101, 01109 Dresden, Germany
 System    |                  Register Court Dresden: HRA 4896
 Research  |              General Partner authorized to represent:
 Center    |             AMD Saxony LLC (Wilmington, Delaware, US)
           | General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy

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diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index fa17d6d..54aa83a 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -1727,6 +1727,12 @@ static void svm_inject_page_fault(struct kvm_vcpu *vcpu,
 
 static int is_disabled(void)
 {
+	uint64_t vm_cr;
+
+	rdmsrl(MSR_VM_CR, vm_cr);
+	if (vm_cr & (1 << SVM_VM_CR_SVM_DISABLE))
+		return 1;
+
 	return 0;
 }
 
diff --git a/drivers/kvm/svm.h b/drivers/kvm/svm.h
index 5e93814..005a9c5 100644
--- a/drivers/kvm/svm.h
+++ b/drivers/kvm/svm.h
@@ -175,8 +175,11 @@ struct __attribute__ ((__packed__)) vmcb {
 #define SVM_CPUID_FUNC 0x8000000a
 
 #define MSR_EFER_SVME_MASK (1ULL << 12)
+#define MSR_VM_CR       0xc0010114ULL
 #define MSR_VM_HSAVE_PA 0xc0010117ULL
 
+#define SVM_VM_CR_SVM_DISABLE 4
+
 #define SVM_SELECTOR_S_SHIFT 4
 #define SVM_SELECTOR_DPL_SHIFT 5
 #define SVM_SELECTOR_P_SHIFT 7

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Re: [PATCH] SVM: reliably detect if SVM was disabled by BIOS

[Avi Kivity]

Joerg Roedel wrote:
> From: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>
>
> This patch adds an implementation to the svm is_disabled function to
> detect reliably if the BIOS disabled the SVM feature in the CPU. This
> fixes the issues with kernel panics when loading the kvm-amd module on
> machines where SVM is available but disabled.
>
>   

Applied; thanks.

Is this msr documented anywhere?  I assume it is implemented on all
processors with svm?

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: [PATCH] SVM: reliably detect if SVM was disabled by BIOS

[Joerg Roedel]

On Fri, Jun 22, 2007 at 12:30:48PM +0300, Avi Kivity wrote:
> Joerg Roedel wrote:
> > From: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>
> >
> > This patch adds an implementation to the svm is_disabled function to
> > detect reliably if the BIOS disabled the SVM feature in the CPU. This
> > fixes the issues with kernel panics when loading the kvm-amd module on
> > machines where SVM is available but disabled.
> >
> >   
> 
> Applied; thanks.
> 
> Is this msr documented anywhere?  I assume it is implemented on all
> processors with svm?

Not in the public documentation yet. But it will be documented with one of
the next documentation updates. This MSR is implemented in all SVM
capable processors.

Regards,

Joerg

-- 
           |           AMD Saxony Limited Liability Company & Co. KG
 Operating |         Wilschdorfer Landstr. 101, 01109 Dresden, Germany
 System    |                  Register Court Dresden: HRA 4896
 Research  |              General Partner authorized to represent:
 Center    |             AMD Saxony LLC (Wilmington, Delaware, US)
           | General Manager of AMD Saxony LLC: Dr. Hans-R. Deppe, Thomas McCoy



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